Fuel management system for variable ethanol octane enhancement of gasoline engines

ABSTRACT

Fuel management system for efficient operation of a spark ignition gasoline engine. Injectors inject an anti-knock agent such as ethanol directly into a cylinder of the engine. A fuel management microprocessor system controls injection of the anti-knock agent so as to control knock and minimize that amount of the anti-knock agent that is used in a drive cycle. It is preferred that the anti-knock agent is ethanol. The use of ethanol can be further minimized by injection in a non-uniform manner within a cylinder. The ethanol injection suppresses knock so that higher compression ratio and/or engine downsizing from increased tubocharging or supercharging can be used to increase the efficiency of the engine.

This application is a continuation of U.S. patent application Ser. No.11/840,719 filed on Aug. 17, 2007, which is a continuation of U.S.patent application Ser. No. 10/991,774, which is now issued as U.S. Pat.No. 7,314,033.

BACKGROUND

This invention relates to spark ignition gasoline engines utilizing anantiknock agent which is a liquid fuel with a higher octane number thangasoline such as ethanol to improve engine efficiency.

It is known that the efficiency of spark ignition (SI) gasoline enginescan be increased by high compression ratio operation and particularly byengine downsizing. The engine downsizing is made possible by the use ofsubstantial pressure boosting from either turbocharging orsupercharging. Such pressure boosting makes it possible to obtain thesame performance in a significantly smaller engine. See, J. Stokes, etal., “A Gasoline Engine Concept For Improved Fuel Economy The Lean-BoostSystem” SAE Paper 2001-01-2902. The use of these techniques to increaseengine efficiency, however, is limited by the onset of engine knock.Knock is the undesired detonation of fuel and can severely damage anengine. If knock can be prevented, then high compression ratio operationand high pressure boosting can be used to increase engine efficiency byup to twenty-five percent.

Octane number represents the resistance of a fuel to knocking but theuse of higher octane gasoline only modestly alleviates the tendency toknock. For example, the difference between regular and premium gasolineis typically six octane numbers. That is significantly less than isneeded to realize fully the efficiency benefits of high compressionratio or turbocharged operation. There is thus a need for a practicalmeans for achieving a much higher level of octane enhancement so thatengines can be operated much more efficiently.

It is known to replace a portion of gasoline with small amounts ofethanol added at the refinery. Ethanol has a blending octane number (ON)of 110 (versus 95 for premium gasoline) (see J. B. Heywood, “InternalCombustion Engine Fundamentals,” McGraw Hill, 1988, p. 477) and is alsoattractive because it is a renewable energy, biomass-derived fuel, butthe small amounts of ethanol that have heretofore been added so gasolinehave had a relatively small impact on engine performance. Ethanol ismuch more expensive than gasoline and the amount of ethanol that isreadily available is much smaller than that of gasoline because of therelatively limited amount biomass that is available for its production.An object of the present invention is to minimize the amount of ethanolor other antiknock agent that is used to achieve a given level of engineefficiency increase. By restricting the use of ethanol to the relativelysmall fraction of time in an operating cycle when it is needed toprevent knock in a higher load regime and by minimizing its use at thesetimes, the amount of ethanol that is required can be limited to arelatively small fraction of the fuel used by the spark ignitiongasoline engine.

SUMMARY

In one aspect, the invention is a fuel management system for efficientoperation of a spark ignition gasoline engine including a source of anantiknock agent such as ethanol. An injector directly injects theethanol into a cylinder of the engine and a fuel management systemcontrols injection of the antiknock agent into the cylinder to centralknock with minimum use of the antiknock agent. A preferred antiknockagent is ethanol. Ethanol has a high heat of vaporization so that thereis substantial cooling of the air-fuel charge to the cylinder when it isinjected directly into the engine. This cooling effect reduces theoctane requirement of she engine by a considerable amount in addition tothe improvement in knock resistance from the relatively high octanenumber of ethanol. Methanol, tertiary butyl alcohol, MTBE, ETBE, andTAME may also be used. Wherever ethanol is used herein if is to beunderstood that other antiknock agents are contemplated.

The fuel management system uses a fuel management control system thatmay use a microprocessor that operates in an open loop fashion on apredetermined correlation between octane number enhancement and fractionof fuel provided by the antiknock agent. To conserve the ethanol, it ispreferred that it be added only during portions of a drive cyclerequiring knock resistance and that its use be minimized during thesetimes. Alternatively, the gasoline engine may include a knock sensorthat provides a feedback signal to a fuel management microprocessorsystem to minimize the amount of the ethanol added to prevent knock in aclosed loop fashion.

In one embodiment the injectors stratify the ethanol to providenon-uniform deposition within a cylinder. For example, the ethanol maybe injected proximate to the cylinder walls and swirl can create a ringof ethanol near the walls.

In another embodiment of this aspect of the invention, the systemincludes a measure of the amour of the antiknock agent such as ethanolin the source containing the antiknock agent to control turbocharging,supercharging or spark retard when the amount of ethanol is low.

The direct injection of ethanol provides substantially a 13° C. drop intemperature for every ten percent of fuel energy provided by ethanol. Aninstantaneous octane enhancement of at least 4 octane numbers may beobtained for every 20 percent of the engine's energy coming from theethanol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of the invention disclosedherein.

FIG. 2 is a graph of the drop in temperature within a cylinder as afunction of the fraction of energy provided by ethanol.

FIG. 3 is a schematic illustration of the stratification of coolerethanol charge using direct injection and swirl motion for achievingthermal stratification.

FIG. 4 is a schematic inspiration showing ethanol stratified in an inletmanifold.

FIG. 5 is a block diagram of an embodiment of the invention in which thefuel management microprocessor is used to control a turbocharger andspark retard upon the amount of ethanol in a fuel tank.

DETAILED DESCRIPTION

With reference first to FIG. 1, a spark ignition gasoline engine 10includes a knock sensor 12 and a fuel management microprocessor system14. The fuel management microprocessor system 14 controls the directinjection of an antiknock agent such as ethanol from an ethanol tank 16.The fuel management microprocessor system 14 also controls the deliveryof gasoline from a gasoline tank 18 into engine manifold 20. Aturbocharger 22 is provided to improve the torque and power density ofthe engine 10. The amount of ethanol injection is dictated either by apredetermined correlation between octane number enhancement and fractionof fuel that is provided by ethanol in an open loop system or by aclosed loop control system that uses a signal from the knock sensor 12as an input to the fuel management microprocessor 14. In bothsituations, the fuel management processor 14 will minimize the amount ofethanol added to a cylinder while still preventing knock. It is alsocontemplated that the fuel management microprocessor system 14 couldprovide a combination of open and closed loop control.

As show in FIG. 1 it is preferred that ethanol be directly injected intothe engine 10. Direct injection substantially increases the benefits ofethanol addition and decreases the required amount of ethanol. Recentadvances in fuel injector and electronic control technology allows fuelinjection directly into a spark ignition engine rather than into themanifold 20. Because ethanol has a high heat of vaporization there willbe substantial cooling when it is directly injected into the engine 10.This cooling effect further increases knock resistance by a considerableamount. In the embodiment of FIG. 1 port fuel injection of the gasolinein which the gasoline is injected into the manifold rather than directlyinjected into the cylinder is preferred because it is advantageous inobtaining good air/fuel mixing and combustion stability that aredifficult to obtain with direct injection.

Ethanol has a heat of vaporization of 840 kJ/kg, while the heat ofvaporization of gasoline is about 350 kJ/kg. The attractiveness ofethanol increases when compared with gasoline on an energy basis, sincethe lower heating value of ethanol is 26.9 MJ/kg while for gasoline itis about 44 MJ/kg. Thus, the heat of vaporization per Joule ofcombustion energy is 0.031 for ethanol and 0.008 for gasoline. That is,for equal amounts of energy the required heat of vaporization of ethanolis about four times higher than that of gasoline. The ratio of the heatof vaporization per unit air required for stoichiometric combustion isabout 94 kJ/kg of air for ethanol and 24 kJ/kg of air for gasoline, or afactor of four smaller. Thus, the net effect of cooling the air chargeis about four times lower for gasoline than for ethanol (forstoichiometric mixtures wherein the amount of air contains oxygen thatis just sufficient to combust all of the fuel).

In the case of ethanol direct injection according to one aspect of theinvention, the charge is directly cooled. The amount of cooling due todirect injection of ethanol is shown in FIG. 2. It is assumed that theair/fuel mixture is stoichiometric without exhaust gas recirculation(EGR), and that gasoline makes up the rest of the fuel. It is furtherassumed that only the ethanol contributes to charge cooling. Gasoline isvaporized in the inlet manifold and does not contribute to cylindercharge cooling. The direct ethanol injection provides about 13° C. ofcooling for each 10% of the fuel energy provided by ethanol. It is alsopossible to use direct injection of gasoline as well as direct injectionof ethanol. However, under certain conditions there can be combustionstability issues.

The temperature decrement because of the vaporization energy of theethanol decreases with lean operation and with EGR, as the thermalcapacity of the cylinder charge increases. If the engine operates attwice the stoichiometric air/fuel ratio, the numbers indicated in FIG. 2decrease by about a factor of 2 (the contribution of the ethanol itselfand the gasoline is relatively modest). Similarly, for a 20% EGR rate,the cooling effect of the ethanol decreases by about 25%.

The octane enhancement effect can be estimated from the data in FIG. 2.Direct injection of gasoline results in approximately a five octanenumber decrease in the octane number required by the engine, asdiscussed by Stokes, et al. Thus the contribution is about five octanenumbers per 30 K drop in charge temperature. As ethanol can decrease thecharge temperature by about 120 K, then the decrease in octane numberrequired by the engine due to the drop in temperature, for 100% ethanol,is twenty octane numbers. Thus, when 100% of the fuel is provided byethanol, the octane number enhancement is approximately thirty-fiveoctane numbers with a twenty octane number enhancement coming fromdirect injection cooling and a fifteen octane number enhancement comingfrom the octane number of ethanol. From the above considerations, it canbe projected that even if the octane enhancement from direct cooling issignificantly lower, a total octane number enhancement of at least 4octane numbers should be achievable for every 20% of the total fuelenergy that is provided by ethanol.

Alternatively the ethanol and gasoline can be mixed together and thenport injected through a single injector per cylinder, thereby decreasingthe number of injectors that would be used. However, the air chargecooling benefit from ethanol would be lost.

Alternatively the ethanol and gasoline can be mixed together and thenport fuel injected using a single injector per cylinder, therebydecreasing the number of injectors that would be used. However, thesubstantial air charge cooling benefit from ethanol would be lost. Thevolume of fuel between the mixing point and the port fuel injectorshould be minimized in order to meet the demanding dynamicoctane-enhancement requirements of the engine.

Relatively precise determination of the actual amount of octaneenhancement from given amounts of direct ethanol injection can beobtained from laboratory and vehicle tests in addition to detailedcalculations. These correlations can be used by the fuel managementmicroprocessor system 14.

An additional benefit of using ethanol for octane enhancement is theability to use it in a mixture with water. Such a mixture can eliminatethe need for the costly and energy consuming water removal step inproducing pure ethanol that must be employed when ethanol is added togasoline at a refinery. Moreover, the water provides additional cooling(due to vaporization) that further increases engine knock resistance. Incontrast the present use of ethanol as an additive to gasoline at therefinery requires that the water be removed from the ethanol.

Since unlike gasoline, ethanol is not a good lubricant and the ethanolfuel injector can stick and not open, it is desirable to add a lubricantto the ethanol. The lubricant will also denature the ethanol and make itunattractive for human consumption.

Further decreases in the required ethanol for a given amount of octaneenhancement can be achieved with stratification (non-uniform deposition)of the ethanol addition. Direct injection can be used to place theethanol near the walls of the cylinder where the need for knockreduction is greatest. The direct injection may be used in combinationwith swirl. This stratification of the ethanol in the engine furtherreduces the amount of ethanol needed to obtain a given amount of octaneenhancement. Because only the ethanol is directly injected and becauseit is stratified both by the injection process and by thermalcentrifugation, the ignition stability issues associated with gasolinedirect injection (GDI) can be avoided.

It is preferred that ethanol be added to those regions that make up theend-gas and are prone to auto-ignition. These regions are near the wallsof the cylinder. Since the end-gas contains on the order of 25% of thefuel, substantial decrements in the required amounts of ethanol can beachieved by stratifying the ethanol.

In the case of the engine 10 having substantial organized motion (suchas swirl), the cooling will result in forces that thermally stratify thedischarge (centrifugal separation of the regions at different densitydue to different temperatures). The effect of ethanol addition is toincrease gas density since the temperature is decreased. With swirl theethanol mixture will automatically move to the zone where the end-gasis, and thus increase the anti-knock effectiveness of the injectedethanol. The swirl motion is not affected much by the compression strokeand thus survives better than tumble-like motion that drives turbulencetowards top-dead-center (TDC) and then dissipates. It should be pointedout that relatively modest swirls result in large separating(centrifugal) forces. A 3 m/s swirl motion in a 5 cm radius cylindergenerates accelerations of about 200 m/s², or about 20 g's.

FIG. 3 illustrates ethanol direct injection and swirl motion forachieving thermal stratification. Ethanol is predominantly on an outsideregion which is the end-gas region. FIG. 4 illustrates a possiblestratification of the ethanol in an inlet manifold with swirl motion andthermal centrifugation maintaining stratification in the cylinder. Inthis case of port injection of ethanol, however, the advantage ofsubstantial charge cooling may be lost.

With reference again to FIG. 2, the effect of ethanol addition all theway up to 100% ethanol injection is shown. At the point that the engineis 100% direct ethanol injected, there may be issues of engine stabilitywhen operating with only stratified ethanol injection that need to beaddressed. In the case of stratified operation it may also beadvantageous to stratify the injection of gasoline in order to provide arelatively uniform equivalence ratio across the cylinder (and thereforelower concentrations of gasoline in the regions where the ethanol isinjected). This situation can be achieved, as indicated in FIG. 4, byplacing fuel in the region of the inlet manifold that is void ofethanol.

The ethanol used in the invention can either be contained in a separatetank from the gasoline or may be separated from a gasoline/ethanolmixture stored in one tank.

The instantaneous ethanol injection requirement and total ethanolconsumption over a drive cycle can be estimated from information aboutthe drive cycle and the increase in torque (and thus increase incompression ratio, engine power density, and capability for downsizing)that is desired. A plot of the amount of operating time spent at variousvalues of torque and engine speed in FTP and US06 drive cycles can beused. It is necessary to enhance the octane number at each point in thedrive cycle where the torque is greater than permitted for knock freeoperation with gasoline alone. The amount of octane enhancement that isrequired is determined by the torque level.

A rough illustrative calculation shows that only a small amount ofethanol might be needed over the drive cycle. Assume that it is desiredto increase the maximum torque level by a factor of two relative to whatis possible without direct injection ethanol octane enhancement.Information about the operating time for the combined FTP and US06cycles shows that approximately only 10 percent of the time is spent attorque levels above 0.5 maximum torque and less than 1 percent of thetime is spent above 0.9 maximum torque. Conservatively assuming that100% ethanol addition is needed at maximum torque and that the energyfraction of ethanol addition that is required to prevent knock decreaseslinearly to zero at 50 percent of maximum torque, the energy fractionprovided by ethanol is about 30 percent. During a drive cycle about 20percent of the total fuel energy is consumed at greater than 50 percentof maximum torque since during the 10 percent of the time that theengine is operated in this regime, the amount of fuel consumed is abouttwice that which is consumed below 50 percent of maximum torque. Theamount of ethanol energy consumed during the drive cycle is thus roughlyaround 6 percent (30 percent×0.2) of the total fuel energy.

In this case then, although 100% ethanol addition was needed at thehighest value of torque, only 6% addition was needed averaged over thedrive cycle. The ethanol is much more effectively used by varying thelevel of addition according to the needs of the drive cycle.

Because of the lower heat of combustion of ethanol, the required amountof ethanol would be about 9% of the weight of the gasoline fuel or about9% of the volume (since the densities of ethanol and gasoline arecomparable). A separate tank with a capacity of about 1.8 gallons wouldthen be required in automobiles with twenty gallon gasoline tanks. Thestored ethanol content would be about 9% of that of gasoline by weight,a number not too different from present-day reformulated gasoline.Stratification of the ethanol addition could reduce this amount by morethan a factor of two. An on-line ethanol distillation system mightalternatively be employed but would entail elimination or reduction ofthe increase torque and power available from turbocharging.

Because of the relatively small amount of ethanol and present lack of anethanol feeling infrastructure, it is important that the ethanol vehiclebe operable if there is no ethanol on the vehicle. The engine system canbe designed such that although the torque and power benefits would belower when ethanol is not available, the vehicle could still be operableby reducing or eliminating turbocharging capability and/or by increasingspark retard so as to avoid knock. As shows in FIG. 5, the fuelmanagement microprocessor system 14 uses ethanol fuel level in theethanol tank 16 as an input to control the turbocharger 22 (orsupercharger or spark retard, not shown). As an example, with on-demandethanol octane enhancement, a 4-cylinder engine can produce in the rangeof 280 horsepower with appropriate turbocharging or supercharging butcould also be drivable with an engine power of 140 horsepower withoutthe use of ethanol according to the invention.

The impact of a small amount of ethanol upon fuel efficiency through usein a higher efficiency engine can greatly increase the energy value ofthe ethanol. For example, gasoline consumption could be reduced by 20%due to higher efficiency engine operation from use of a high compressionratio, strongly turbocharged operation and substantial enginedownsizing. The energy value of the ethanol, including its value indirect replacement of gasoline (5% of the energy of the gasoline), isthus roughly equal to 25% of the gasoline that would have been used in aless efficient engine without any ethanol. The 5% gasoline equivalentenergy value of ethanol has thus been leveraged up to a 25% gasolineequivalent value. Thus, ethanol can cost roughly up to five times thatof gasoline on an energy basis and still be economically attractive. Theuse of ethanol as disclosed herein can be a much greater value use thanin other ethanol applications.

Although the above discussion has featured ethanol as an exemplaryanti-knock agent, the same approach can be applied to other high octanefuel and fuel additives with high vaporization energies such as methanol(with higher vaporization energy per unit fuel), and other anti-knockagents such as tertiary butyl alcohol, or others such as methyl tertiarybutyl ether (MTBE), ethyl tertiary butyl ether (ETBE), or tertiary amylmethyl ether (TAME).

It is recognized that modifications and variations of the inventiondisclosed herein will be apparent to those of ordinary skill in the artand it is intended that all such modifications and variations beincluded within the scope of the appended claims.

1-32. (canceled)
 33. A spark ignition engine where a first fuel isintroduced into the engine by a first fuel injector and a second fuel isintroduced into the engine by a second fuel injector where the secondfuel has a higher octane number than the first fuel and where the secondfuel is introduced into the engine by a second fuel injector thatintroduces at least some of the second fuel as a liquid into a least oneengine cylinder: and where the ratio of the amount of fuel introducedinto the engine by the second fuel injector to the amount fuelintroduced into the engine by the first fuel injector increases withincreasing torque.
 34. The spark ignition engine of claim 1 where thefirst fuel is introduced into the engine cylinder by port fuelinjection.
 35. The spark ignition engine of claim 1 where the engine canbe operated on the second fuel alone.
 36. The spark ignition engine ofclaim 1 where the fuel-air ratio is substantially Stoichiometric.
 37. Aspark ignition engine where a first substance which is a fuel isintroduced into the engine by a first means: and where a secondsubstance which includes water is introduced as a liquid by directinjection into at least one engine cylinder and provides vaporizationcooling of the air charge in the cylinder; and where the ratio of secondsubstance to first substance introduced into the engine increases withincreasing torque.
 38. The spark ignition engine of claim 37 where theratio of the second substance to the first substance increases so as toprevent knock.
 39. The spark ignition engine of claim 37 where the ratioof the second substance to the first substance is determined by closedloop feedback control using a knock detector.
 40. The spark ignitionengine of claim 37 where the ratio of the second substance to firstsubstance is determined by a open loop control.
 41. The spark ignitionengine of claim 37 further including it fuel management system where thefuel management system minimizes the amount of second substance that isused.
 42. The spark ignition engine of claim 41 where the fuelmanagement system uses a microprocessor.
 43. The spark ignition engineof claim 37 where the second substance provides greater vaporizationcooling of a fuel air mixture in the cylinder than the first substance.44. The spark ignition engine of claim 37 where the water is injectedinto the engine in a mixture with another liquid.
 45. The spark ignitionengine of claim 37 where the first substance is introduced into theengine manifold.
 46. The spark ignition engine of claim 37 where thesecond substance is injected so as to have a higher concentration in theend gas region.
 47. The spark ignition engine of claim 46 where thesecond substance is injected so as to have a higher concentration nearthe periphery of the cylinder.
 48. The spark ignition engine of claim 37where the first substance is gasoline.
 49. A spark ignition engine wheregasoline and water are directly injected into at least one enginecylinder and where the water to gasoline ratio increases with increasingtorque.
 50. The spark ignition engine of claim 49 where the water togasoline ratio is varied so as to prevent knock.